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9 Feb 2016

Meet pesticides, the silent bird killers that protect our crops

Pesticide usage in farming is responsible for millions of bird deaths annually. Intensive agriculture will make it worse. Photo: Andy Hay/RSPB

By Sanya Khetani-Shah

The illegal killing of birds with poisoned baits and their accidental deaths from pesticides occurs on a global scale: Tens of millions have died, leading to a decline in numerous species’ populations.

Birds of prey are targeted with poison baits if they are seen as predators by racing-pigeon enthusiasts, gamekeepers, livestock farmers, poultry farmers and fishermen. But what’s worse is that many times the birds are not even the intended target. They are often also accidental victims of pesticides targeted at mammalian predators (such as rodents, feral cats and foxes) and insects by farmers to protect livestock and harvests.

Pesticide problems

If current intensive farming trends continue, pesticide usage will likely grow. And while the availability of pesticides for farming is generally regulated at a national and EU level, some countries do not require the effects of pesticides on birds to be considered before they are registered.

Birds of prey such as Black Kites and buzzards that feed on pesticide-affected locusts and earthworms respectively are at risk of unintentional poisoning from organophosphates and carbamates (the most common insecticides). One studyhas estimated that pesticides accidentally kill between 0.25 and 8.9 birds per hectare of agricultural area each year.

Even if the birds don’t ingest enough pesticide to kill them, small amounts of these chemicals can cause sub-lethal effects. Raptors can lose the ability to fly until paralysis of the respiratory muscles causes death. Migratory birds also become lethargic, a death sentence to species dependent on flying great distances to survive.

Lack of awareness among users of these chemicals can thwart any attempts by authorities to mitigate their ill effects on nature. Carbofuran, earlier used worldwide for crop pest control, has now been restricted or banned in most of Europe. But as the cover storyof the February issue of our newsletter Birdseye shows, it is still easily attainable for farmers who are unaware of its toxic effects on birds.

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Migratory birds are also exposed to various rodenticides used in agriculture when they eat either poisoned baits or poisoned prey. Many raptor and scavenging species such as the Red Kite and buzzards are especially at risk due to a regular diet of rodents, voles and their carcasses. The lack of protection of bait stations, broadcast baiting and failure to remove bait at the end of baiting campaigns increase the risk of exposure to birds.

Between 2009 and 2011 in Norway, 70% of Golden Eaglesand 50% of Eurasian Eagle Owls had ingested anticoagulant rodenticides (ARs, the most widely used). In 2010, ARs were detected in 90% of Barn Owls, Red Kites and kestrels in the UK and 44% of Red Kites in France. Sub-lethal exposure to rodenticides can hinder the recovery of birds of prey from non-fatal collisions and cause lethargy, which impairs their hunting ability and increases the risk that they will starve.

Poison bait danger

Poison baits (in the form of animal carcasses or parts laced with toxins) are used either to kill predators such as wolves and foxes (with birds of prey being accidental victims) or used directly against birds of prey, for example by hunters seeing them as competitors. This happens despite the use of poison baits to control predators being illegal in Europe under the Bern Convention and the EU Birds Directive. The illegal use of poison is among the most important direct threats in Europe to the Spanish Imperial Eagle, the Eastern Imperial Eagle, the Red Kite, and the Egyptian Vulture.

In Hungary, the mortality of birds of prey due to poisoning has markedly increased since 2007: between 2000 and 2015, illegal carbofuran (earlier used worldwide as a pesticide, now banned in most of Europe because of its toxicity) was detected in 85% of the 476 birds found poisoned by baits used to illegally control predators. In Greece, poisoning has resulted in the decline of the Bearded Vulture. Similar problems exist in the Netherlands, Croatia, Austria and the Czech Republic. An analysis of 267 non-natural deaths of Spanish Imperial Eagles in Spain between 1989 and 2004 found that 31% were caused by poisoning.

It is clear that we are far from completely stopping the use of poisoned baits. Enforcement is often inadequate because many government departments are understaffed and ill equipped, and the punishment sentences given are too low to be a deterrent.

Putting an end to these kind of poisoning cases – especially when it comes to birds that depend on farms to breed and feed – is not easy, and not just because it is difficult to catch a poisoner with a ‘smoking gun’, so to speak.